If you run a website, you already know that video can be heavy. WebM is a format made for the web, and it usually gives you a lighter file than a plain MP4 for the same picture. That makes pages load faster and saves your visitors data.
This page lets you convert MP4 to WebM in your browser, without uploading the clip. Below you will see what the tool does to your picture and sound, what to choose for Quality, and when it is better to stay with MP4.
How to convert MP4 to WebM
- Drop your MP4 onto the tool above.
- Check that "Convert to" shows WebM. The tile reads "VP9. Smaller, for the web".
- Pick a Quality. Each option shows the estimated size of the WebM.
- Keep the sound on, unless the clip is meant to be silent, such as a background loop.
- Press Convert and save your WebM.
It is free, with no account and no watermark. Video tools are not part of the free daily limit, which covers document conversions only.
What happens to the picture and sound
Unlike a repackage between MP4 and MOV, going to WebM always re-encodes the video. The tool writes the picture as VP9 where your browser is able to encode it, and as VP8 where it is not. The sound is written as Opus. All of this runs in your browser, on your own computer.
Because of the re-encode, the Quality control always matters on this page. The usual "copied as it is" shortcut does not apply to WebM, so expect the job to take longer than a quick repackage.
| Your MP4 | The WebM | |
|---|---|---|
| Picture | Usually H.264 | VP9, or VP8 where needed |
| Sound | Usually AAC | Opus |
| Process | Left as it is | Re-encoded |
| Best at | Playing everywhere | Video on web pages |
Which Quality should you choose?
Balanced is the right start for a website clip. Compare the sizes on the three options: Smaller gives the lightest file, Best keeps the most detail. For a hero video on a page, try Balanced and view the result before you publish. If the file is still heavier than you want, the Smaller option or the compress video tool will help.
VP9 or VP8: which one will you get?
VP9 is the newer of the two and usually gives a lighter file for the same picture. The tool uses it whenever your browser is able to encode it. If your browser cannot, the tool falls back to VP8, which is older and plays in the same places. You do not have to choose, and the Convert button works the same either way.
If you want to be sure of the result, convert a short test clip first and look at the file size and the picture. It takes seconds and tells you what a full-length conversion will look like.
When WebM is the right choice, and when it is not
WebM shines on web pages. Current Chrome, Edge and Firefox play it directly, so you can embed it with a standard video tag and know that most visitors will see it. It is also a good fit for short background loops and product clips where file size matters.
It is a poor choice for sharing with people. Many editors, phones and televisions do not handle WebM well. For those jobs, keep the MP4. If someone asks you for a video file and does not say which format, MP4 is almost always the safer answer, and WebM is the one you choose on purpose for a page you control.
- Use WebM for: website banners, short product demos, looping backgrounds and page embeds.
- Keep MP4 for: messaging apps, social uploads, TV playback and editing.
- A common approach: publish both files, and let the page offer WebM first with MP4 as the backup.
On a page, WebM also avoids a problem that large MP4 files can cause: a slow start. A lighter file begins to play sooner, particularly on a mobile connection. That is the practical reason web designers reach for it, and it is why this conversion is worth a minute of your time before a launch.
Preparing a clip for your website
The file size of a web video depends on three things: how long it is, how big the picture is and how much detail you keep. You control all three. The converter handles the last one, and other tools handle the first two.
- Trim the clip to the part you need.
- If the frame is larger than the space on the page, shrink it with resize video.
- Convert to WebM with Balanced quality.
- Look at the estimated size, and try Smaller if the page needs to be lighter still.
- Test the result in a browser before it goes live.
A WebM that is far larger than the MP4 you started with is a sign that the source was already well compressed. In that case there is little to gain, and you may be better off leaving the MP4 on the page. The size estimates under the Quality options let you spot this before you spend the time converting. Your source MP4 is never changed. You get a new WebM file next to it, and you can run the conversion again at a different Quality whenever you want.
Speed, limits and privacy
MP4 files are handled the fast way, with no size limit. The note beside the Convert button reads "Fast, on this device. Nothing uploaded". Re-encoding takes processor time, so a long or high-resolution clip will take a while, and it is worth keeping the tab open. Several files can be dropped in together and downloaded as a zip when they are done, which suits a set of page clips that should all share the same settings.
Your video is never uploaded. The server does no video work. See the privacy page for the details, and the main convert video page for other formats. The tool runs in current Chrome, Edge and Firefox.
Make your web video lighter
To convert MP4 to WebM, drop your clip into the tool above, pick a Quality and press Convert. You get a VP9 or VP8 picture with Opus sound, made on your own device.
Need to go the other direction? See WebM to MP4 for the reverse conversion.
